Table 3. Association of Severity of Sun-Damaged Skin With cSCC in 220 236 Patients With 19 620 Cases of cSCC .
| Proxy for severity of sun-damaged skin | Prevalence, %a | Follow-up, median (IQR), y | No. of patients with a cSCC | Proportion of total cSCCs, % | cSCC incidence per 100 person-years (95% CI) | Subdistribution HR (95% CI)b |
|---|---|---|---|---|---|---|
| No. of AKs removed with cryotherapy | ||||||
| 1 | 35.5 | 4.4 (2.0-7.4) | 5503 | 28.0 | 1.47 (1.43-1.51) | 1 [Reference] |
| 2 | 19.3 | 4.9 (2.3-7.8) | 4807 | 24.5 | 2.22 (2.15-2.28) | 1.30 (1.25-1.36) |
| 3-14 | 11.3 | 4.1 (1.8-6.8) | 3338 | 17.0 | 2.93 (2.83-3.03) | 1.55 (1.49-1.62) |
| ≥15 | 2.0 | 4.7 (2.1-7.2) | 751 | 3.8 | 3.52 (3.27-3.77) | 1.89 (1.75-2.04) |
| Cryotherapy, No. unspecified | 18.6 | 3.5 (1.6-6.2) | 2535 | 12.9 | 1.53 (1.47-1.59) | 1.09 (1.04-1.14) |
| Field therapy | 2.9 | 3.4 (1.4-6.7) | 558 | 2.8 | 2.11 (1.94-2.29) | 1.42 (1.30-1.55) |
| Cryotherapy and field therapy | 4.8 | 3.5 (1.5-6.6) | 1267 | 6.5 | 2.84 (2.69-3.00) | 1.83 (1.72-1.95) |
| No therapyc | 5.6 | 4.3 (1.9-7.2) | 861 | 4.4 | 1.50 (1.40-1.60) | 1.05 (0.97-1.13) |
Abbreviations: AK, actinic keratosis; BCC, basal cell carcinoma; cSCC, cutaneous squamous cell carcinoma; HR, hazard ratio; IQR, interquartile range.
a
The analysis is restricted to patients with AK and does not include general population control patients.
b
The Cox proportional hazards regression model includes year of AK visit, age, sex, race/ethnicity, and history of BCC as coded in Table 2.
c
We reviewed a convenience sample of 10 medical records from this group, noting that the reason for not receiving therapy was typically patient preference or a decision to wait (eg, until after a wedding). The numbers of AKs in this group were not recorded systematically and could not be analyzed.